The objectives of this project are to determine the influence of microwave radiation on cardiac tissue in vitro and in vivo. The influence of microwave radiation during embryogeny on the development of cardiac tissue was determined. No effects were noted on the morphological or biochemical parameters measured for Japanese quail myocardium in embryos exposed to 5 or 20 mW/square cm during the first 8 days of development. Techniques for exposing isolated rat atria to microwave radiation have been developed. The rate and force of contraction will be monitored and the responsiveness of the tissue to drugs during microwave exposure will be determined. Also, certain biochemical and physiological parameters which are indicative of cardiac function will be measured in unanesthetized rats during whole body exposure to 2450 MHz microwaves. The parameters measured include plasma creatine phosphokinase activity, electrocardiogram and blood pressure during 4 hours exposure to microwaves at 5 and 10 mW/square cm. No data is available on these two areas of study.